This invention relates to an elevator safety device.
In elevator systems the elevator car might stop midway between a pair of adjacent floors of a building served by the car and confine passengers therein. Without the car enabled to arrive at its desired floor. Alternatively the elevator car might rush at a high speed into a top or a bottom terminal floor. One of the reasons for this has been the occurrence of the bad electrical conduction on one portion of the main circuit arranged to safely supply to an associated electric hoist motor an electric power required for the elevator car to travel in the upward or downward direction. As the main circuit has many electric components serially interconnected, the same includes a multiplicity of terminals and the like connecting those components to one another. If contacting would have been deteriorated at any of the terminals by some rare accident then heat will be excessively generated at the deteriorated contact portion to fuse it. Accordingly the fused portion increases in resistance resulting in a fault that the electric motor becomes difficult to be smoothly supplied with the electric power.
As a result, elevator systems without the feedback control have shown signes that the landing accuracy decreases and/or passengers are uncomfortable to ride in the elevator car. This has aroused an attention of passengers or elevator service men. Therefore such a fault has easily been found before the control is disabled by the fully fusion of the bad contact portion. In feedback control elevator systems, however, the control system has been first operated to compensate for the increase in resistance as above described through the feedback control until the control is disabled upon the full fusion of the resistance increased portion. Thus the elevator car has increased in speed by means of an unbalanced force caused from the load to actuate an associated governor. This has resulted in an emergency that the elevator car stops midway between a pair of adjacent floors of a building served by the car and confines passenger therein. Alternatively the elevator car might rush into the top or bottom terminal floor while it is maintained at high speed resulting in large shocks giving the passengers. Thus the service men have frequently tended to find no fault as above described until the occurrence of the above-mentioned emergency. Particularly, upon the occurrence of an emergency that the elevator car has stopped midway between a pair of adjacent floors, an urgent expedient manually performed in the operation of rescuing the passengers from the elevator car stopped midway between a pair of adjacent floors has resulted in the car only falling down through the drawing-down due to a loading on the car. Thus the car has been impossible to be moved in the desired direction. Consequently, if the rescue operation is erroneously performed while the rescue persons do not know the break of the main circuit with the hoist motor for the car then it can not be said that there will be no danger that the elevator car would have fallen down.
There have been already proposed elevator safety devices for sensing the break of the main circuit for driving elevator cars. In known safety devices, the speed comparator involved might not be operated immediately in response of the sensed break of the main circuit and dependent upon what load is imposed on the elevator car. This has cooperated with an ergency terminal speed limiting device disposed on either of the top and bottom terminal floors to cause a great failure such as damage to an associated buffer.
Accordingly it is an object of the present invention to provide a new and improved elevator safety device ensuring that an elevator car is prevented from accelerating to dangerous speed upon the break of the main circuit for driving the car.